This invention relates to a compact and portable detection device for nitrogen base explosive chemical compounds, such as TNT. The portable device can be conveniently carried by an individual, is extremely sensitive to the class of compounds being detected, and is minimally affected by potential interfering substances.
The device of the present invention is based upon the use of fiber optic spectroscopy. Sensors to detect light emitted from an optical fiber can be constructed that are sensitive, compact, readily portable, and require a minimum of training for their use. The preferred process of the invention relies upon a chemical system, and optical and electronic components to monitor a decrease in fluorescence when a subject molecule (such as TNT) interacts with fluorescent polycyclic aromatic
Fluorescence is a process by which an atom or molecule emits radiation as a result of the absorption of radiation from another source. In most cases, the transmitted longer wavelength than the absorbed radiation. In the case of most organic molecules, both the absorption and emission radiation wavelengths are in the ultra-violet to visible regions of the spectrum. A variety of materials exhibit fluorescent properties. Some examples of these include fluorescent crystals such as zinc or cadmium sulfide are used in lamp tubes, television screens, scintillation counters, and similar devices. Fluorescent dyes are used for labeling molecules in biochemical research.
Current explosive detection methods utilize neutron beams and energy detection to characterize the organic compounds under surveillance. U.S. Pat. No. 4,882,121, issued Nov. 21, 1989, discloses a neutron generator for supplying neutrons to an object which may to contain an explosive, and a germanium detector and analysis means coupled to the detector which is able to analyze the fast gamma photons emitted by the object and trapped by the detector. The system then determines the nitrogen/oxygen ratio in the object, so that this ratio can be compared with that of the explosive and establish whether the object contains the explosive. A second patent, U.S. Pat. No. 3,997,787, issued Dec. 14, 1976, discloses an apparatus and method for detecting the presence of nitrogen and oxygen-containing explosives within a container by irradiating the container with thermal and high-energy neutrons, and then measuring the quantity of thermal energy neutrons passing through the container and the quantity of radioactive nitrogen 16 generated within the container. The measurements of neutron absorption and nitrogen 16 are correlated to provide an output signal indicative of whether the material within the container is an explosive. A third patent, U.S. Pat. No. 3,146,349, issued Aug. 25, 1964, discloses a method for detecting explosives in luggage in which the explosives have been seeded with a high cross-section neutron absorber by placing a low level thermal neutron source along one side of the luggage. The source having a sufficiently low flux density as to be non-destructive to the contents of ordinary luggage including photographic film, irradiates the luggage with thermal neutrons. By placing a gamma ray detector on the other side of the luggage and comparing the amount of gamma rays emitted directly by the absorber with background gamma rays, it provides an indication of the presence of an explosive.
Although the above devices may be effective, they are too massive, non-portable, and, because of the neutron and gamma radiation, cannot be used near humans without effective shielding, i.e., lead, water or polyethylene.
Dogs can also be trained to sniff out explosives, but the drawbacks are that they require a trainer/handler and have a limited attention span.
The present invention provides a simpler, less expensive, portable device that can be used virtually anywhere including close proximity to humans.